The present invention, relates to a process for forming a thin polymer film on solid particulate material.
The present invention, more particularly relates to process for forming a thin polymer film on solid particulate material used in abrasive blast cleaning.
Abrasive blast cleaning is used for various purposes, including the removal of rust and paint from work surfaces, or roughening the surfaces of work pieces, prior to painting, or coating the surfaces, or removing burrs and flash from molded parts, or cutting, and/or carving, selected areas in glass.
The abrasive particles used in abrasive blast cleaning, are selected, in accordance with the work piece material, and its size and shape. Other factors are the finish desired, and the nature of the material to be removed from the work piece, e.g., rust, scale, or paint. Abrasives are commonly formed from such materials as metallic grit, metallic shot, silica, sand, glass, staurolite, garnet, coal slag, walnut shells, plastic beads, aluminum oxide, silicon carbide, and cut wire. The preceding materials are typically grouped as manufactured, naturally occurring, or mineral slag, abrasives.
The abrasive particles will have various diameters, or sizes, depending on the work piece material, and desired finish. Typically, the particle diameter will vary between about two one-thousandths (0.002) of an inch and about one-half (0.5) of an inch. The particles can be spherical, or sharp-edged, depending on the process used to form the particles. In general, a smaller size particle will produce a smoother surface finish, whereas a larger size abrasive particle will produce a rougher surface. The abrasive impact force of the particle is a factor in the cleaning action. The impact force is a function of the particle size, and particle density, i.e., larger and denser particles, will have a greater impact force, and a more efficient abrasive cleaning action.
The abrasive particles can be propelled against the work piece, by means of an airless, abrasive, blast wheel, or a pressure blast nozzle.
One problem associated with abrasive blast cleaning is the formation of fine dust, due to breakdown, or fracture of the abrasive particles, e.g., by the impact of one particle against another, i.e, impact against substrate or removal of substrate. Premature formation of the fine particle dust is undesirable, in that it adds dust to the environment, reduces the service life of the abrasive material, and increases the dust disposal costs. Also, the fine dust must be removed from the usable abrasive particles, before the particles are recycled back through the propelling device, i.e., the blast wheel or blast nozzle. Further, the fine particle dust poses the possibility of an explosion.
Another problem with presently known abrasive particles, is that, for certain types of work pieces, the particles do not have the desired combination of absorption surface hardness, and density. In some situations, it is desired that the abrasive particle have a relatively soft surface, while at the same time having a relatively high density. The soft particle surface is necessary, to produce a relatively smooth surface finish, on the work piece. Softer abrasive particles are, also, less destructive to the walls of the propelling device. A relatively high abrasive particle density is desirable, in that it contributes to a higher impact force, and a quicker, more efficient, cleaning action. As stated above, materials commonly used for the abrasive particles do not have the desired combination of soft, i.e., low, surface hardness, and a high density.
Such materials as staurolite, garnet, steel shot, and ground glass have a relatively high density. However, such materials have a relatively high surface hardness. Materials such as, walnut shells, corn cobs, and plastics, have a relatively soft, or non-aggressive, surface. However, such materials have a relatively low density.
The use of various resin particles as abrasive blast cleaning media is known. For example, U.S. Pat. No. 4,545,155, issued to J. Nakata, discloses a method of abrasive blast cleaning wherein the abrasive media comprises a slurry, containing a synthetic resin abrasive, water, and a non-ionic surfactant.
U.S. Pat. No. 3,313,067, issued to D. Smith et al., discloses a cleaning method, wherein discrete particles of polycarbonate resin are used as the blast cleaning agent.
U.S. Pat. No. 4,731,125, issued to L. Carr, discloses the use of urea formaldehyde particles as a blast cleaning media.
The present invention relates to a process for forming abrasive particles, wherein the absorption density and surface hardness can be independently controlled. For example, under the present invention, it is possible to obtain a particle having a high density, low surface hardness, and the capability of absorption.
Prior art, as in U.S. patent application, Ser. No. 07/757,977, (now allowed as U.S. Pat. No. 5,256,703), taught the art of imbedding abrasives in urethane foam, to prevent fracture and absorb dust. The prior art was limited to abrasive inorganic, minerals, 66% solids filler, and was unusable in conventional abrasive blast machines.
The present invention also relates to a process to form a thin film of polymer on solid particulate, where the polymer film contains a third component active ingredient.
The present invention further relates to formation of a thin polymer film onto absorbent particulates, pretreated with absorbate, so as to allow the slow release of the absorbate.